303
FXUS02 KWBC 291954
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
354 PM EDT Tue Sep 29 2026

Valid 12Z Fri Oct 02 2026 - 12Z Tue Oct 06 2026


...Major Multi-day South-Central to East-Central U.S. Excessive
Rainfall/Flooding threat this week with tropical connections...


...Guidance/Predictability Assessment...

The latest 00/06/12Z guidance remains fairly agreeable on the
overall synoptic pattern through the period. An initial upper-wave
departing the East Coast will leave a trailing frontal boundary
meandering through the Southeast to south-central U.S. before
eventually progressing south as another upstream upper-
wave/trailing cold front approaches from the northwest. Guidance
agrees this upper-wave will amplify over the eastern U.S. and drive
the surface fronts further south towards the Gulf by mid-next
week. Meanwhile, another upper-wave upstream will bring another
frontal system along the northern tier towards the north-central
U.S. with good guidance agreement and continuity for this late into
the period. The greatest uncertainty during the period looks to
remain related to the progression of both frontal boundaries which
will impact the location/coverage of the anticipated heavy rainfall
through the period. The 13Z NBM initially provides a good
compromise between the deterministic/AI/mean guidance with the QPF
footprint across the southern Plains to Lower Miss/Tenn Valleys
Friday/Saturday. However, thereafter, the GEFS mean remains more
aggressive particularly with the northern extent of QPF coverage
from the Tennessee Valley/Appalachians and into the Mid-Atlantic
which leads to higher totals further north in the NBM compared to
the rest of the guidance. Ultimately favored a compromise between
the NBM and ECens mean across these locations late weekend into
early next week. The rest of the updated WPC forecast package used
a composite blend of the best clustered deterministic/AI guidance
(GFS/ECMWF/UKMET/ECMWF AIFS/AI GFS) through the first half of the
period. An initially small contribution from the GEFS/ECens mean is
ramped up to 40% of the blend by day 7/Tuesday given some
increasing deterministic spread, though all guidance continues to
remain fairly well clustered overall given the lead time.


...Pattern Overview and Weather/Hazards Highlights...

A closed upper trough/low with wavy frontal systems will shift
slowly eastward over the South-central U.S. later week in southern
stream split flow. Widespread excessive rainfall/flooding threats
over the South-central U.S. will slowly shift across the East-
central/Southern U.S. as further focused by Gulf/Southeast Coast
frontal genesis. This event will be fueled by a tropical moisture
connection from current East Pacific Hurricane Polo which will
weaken as it tracks through Northwest Mexico. There will also
develop an increasingly deep and protracted lead Gulf inflow
pattern with tropical influence. This expansive multi-day threat
should prove slow to progress late week wedged between upper ridges
over the Southwest and Southeast U.S.. Activity focus will then
slowly work downstream into the East. Expansive WPC Excessive
Rainfall Outlook Marginal Risk areas with embedded Slight Risk
areas cover the Southern Plains through the Tennessee Valley and
Central Gulf Coast states then into the Appalachians and vicinity
for the Day4/Friday and Day5/Saturday periods.

Meanwhile, systems within a more progressive/zonal mean northern
stream flow will support passage of a series of wavy frontal
systems across the U.S. northern tier of the nation from the
Northwest through the Northeast this week. These will act to
provide a northern rainfall shield focus and over-running for
lifting moisture/clouds and deliver moderating post-frontal fall
temperatures to spread/sink southward with high pressure settling.
This scenario will also act to focus/confine a lead heavy rainfall
main threat axis to The South and the Southeast early next week.
Activity will progress slowly from the East-central U.S. to the
East later period with the greatest confidence in additional heavy
rainfall shifting from the Southern Plains/Lower Mississippi Valley
into the Tennessee Valley/southern Appalachians/southern Mid-
Atlantic and then eventually to the southeast Atlantic/Gulf Coasts
with southward frontal progression. These EROs and supporting WPC
Hazards Outlook areas are all linked below.

Upper-ridging will lead to a period of above-average temperatures
over the western U.S. including highs into the 90s and low 100s for
central/southern California and the Desert Southwest. Some heat
may reach hazardous levels for southern California this
weekend/early next week.


Putnam/Schichtel


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key Messages
are at:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw


























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